The present invention relates to a magnetic bubble device and, more particularly, to bubble propagation paths of an ion-implanted bubble device in which the bubble propagation paths are made in a layer of magnetic material by ion-implantation.
In recent years, a number of approaches have been proposed for the realization of a high density storage magnetic bubble memory device in which the bit period is 4 .mu.m or less, and the memory capacity is 4 Mbits or more. A very promising proposal is the ion-implanted bubble device which is well known in the art.
On the other hand, the most popular bubble propagation organization for the ion-implanted bubble device is a major-minor organization which comprises a plurality of minor loops and one or two major lines (or loops). The bubble is transferred by a transfer gate between the minor loop and the major line. However, the minor loop of prior art has a linear formation which is inconvenient from the viewpoint of design as well as performance of the transfer gate so far as a high density device is concerned. Such a formation of the minor loop also disadvantageously limits an improvement of the storage density.
To solve these problems, it is preferred to adopt the folded minor loop organization which has usually been employed in conventional permalloy bubble devices. In this folded minor loop organization, the loop has conventionally been folded, for example, in a U- or h-shaped. However, such folded minor loops must have, as will be described more in detail later, in addition to a plurality of 180.degree. outside turns, at least one 180.degree. inside turn along the bubble propagation path. No 180.degree. inside turn of the bubble propagation path having good performance characteristics and requiring no large space has been realized by ion-implantation. Accordingly, it has been impossible to realize an ion-implanted bubble device adopting the folded minor loop organization.